JP2024508943A - Solenoid for air delivery system - Google Patents

Abstract

The method includes applying an actuation voltage to the solenoid for a first period of time to actuate the solenoid against energization. The method includes reducing a voltage applied to the solenoid to a holding voltage that is less than an actuation voltage to hold the solenoid against energization during a second period of time. A solenoid has a coil to which an actuation voltage and a holding voltage are applied. The coil is rated for continuous operation at rated voltage. The working voltage exceeds the rated voltage.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Patent Application No. 63/158,090, filed March 8, 2021, the contents of which are incorporated herein by reference in their entirety. is incorporated herein.

FIELD This disclosure relates to solenoids, and more specifically to solenoid valves such as those used in air delivery systems.

Description of Related Art Insufflation devices and gas-tight trocar systems commonly employ solenoids to control gas flow. These solenoids inherently generate thermal energy when electrically energized due to the electrical resistance of the coil wire. This heat typically must be dissipated through the use of cooling fans, which further burdens the system due to additional power requirements, increased size, and increased weight. Modern operating rooms are continually challenged by the increasing amount of medical electrical equipment used for surgical procedures, and this equipment consumes space and power and also poses a risk of musculoskeletal injury. present to personnel, who must constantly lift and cycle the equipment between procedures. Therefore, there remains a continuing need for smaller, lighter, and more electrically efficient medical devices.

The solenoids used in insufflation devices and gas-tight trocar systems are typically numbered 3 to 9 and contribute substantially to the overall system size, weight, and power consumption. As pressure and flow requirements increase, solenoid size also increases. This phenomenon is related to the solenoid force required to displace the poppet which increases as the pressure or pressure area acting on the poppet increases.

Conventional techniques have been considered satisfactory for their intended purpose. However, there is always a need for improved systems and methods for smaller, lighter, and more efficient solenoids and solenoid valves. This disclosure provides a solution to this need.

The method includes applying an actuation voltage to the solenoid for a first period of time to actuate the solenoid against energization. The method includes reducing the voltage applied to the solenoid to a holding voltage that is less than the actuation voltage to hold the solenoid against energization during a second period of time. A solenoid has a coil to which an actuation voltage and a holding voltage are applied. The coil is rated for continuous operation at rated voltage. The working voltage exceeds the rated voltage.

The holding voltage may be lower than the rated voltage. application of actuation voltage to the solenoid after the energization is relaxed and the voltage applied to the solenoid has dropped below the holding voltage for a period of time while the coil is cooled to the first temperature; can be carried out. During the second period, the coil may be raised to a second temperature. The first period can be short enough such that the coil does not exceed the second temperature during the first period. The actuation voltage can be higher than the rated voltage, but the first period can be short enough to apply the first voltage without introducing a failure mode to the coil. Here, the failure mode includes at least one of dielectric breakdown, melting or distortion of the housing or bobbin, or seizure of the armature. At least one of the actuation voltage and holding voltage may be applied as an alternating current waveform whose average is the respective actuation voltage and/or holding voltage.

The solenoid can be operably connected to the valve having an open position to allow flow through the valve and a closed position to prevent flow through the valve. The biasing can bias the valve to an open position. Activating the solenoid against the bias can actuate the valve to the closed position. By holding the solenoid against bias, the valve can be held in a closed position. The method includes reducing the voltage below a holding voltage in response to excess pressure in the air line, thereby energizing the valve to open to an open position to relieve the excess pressure in the air line. can include. It is also contemplated that the method may include reducing the voltage to zero in a power loss event, thereby energizing the valve to open to the open position and relieving pressure within the surgical cavity of the patient. be done. The method can include filtering flow through the valve in the open position to reduce or prevent particles from passing through the valve.

For example, the actuation voltage may be 48 volts and the holding voltage may be 5 volts. Applying the actuation voltage may include applying 20 watts to the solenoid, and holding the solenoid against energization for a second period of time may include, for example, applying 1 watt at the holding voltage. This includes applying voltage to the solenoid.

The solenoid includes a coil seated within a housing. An armature extends longitudinally through the coil and out of the first end of the housing. The armature includes a material that is responsive to an external magnetic field and is mounted within the housing for movement relative to the coil and housing in response to the magnetic field of the coil. The latch member is mounted to the second end of the housing and includes a latch surface configured to contact the armature with the armature in the retracted position. A plurality of permanent magnets are circumferentially distributed around the armature at the first end of the housing.

The latch member is threadably engageable with the housing to adjust the axial position of the latch surface within the housing by rotating the latch member relative to the housing. There can be four permanent magnets distributed circumferentially around the armature. The polarity of each permanent magnet can be oriented radially relative to the longitudinal direction. For each permanent magnet, the radially inner pole can be magnetic south and the radially outer pole can be magnetic north. The coil may be wound around the outwardly facing surface of the bobbin of the housing, and the inwardly facing surface of the bobbin engages the armature as a sliding bearing surface.

The system includes a solenoid having a coil seated within a housing. An armature extends longitudinally through the coil and out of the first end of the housing. The armature includes a material that is responsive to an external magnetic field and is mounted within the housing for movement relative to the coil and housing in response to the magnetic field of the coil. A controller is operably connected to control the coil. The controller is configured to apply an actuation voltage to the coil to actuate the solenoid against the energization during a first period of time and to hold the solenoid against the energization during a second period of time. including machine-readable instructions configured to apply a lower voltage to the solenoid to a holding voltage lower than the actuation voltage, and the coil is rated for continuous operation at the rated voltage. , and the operating voltage exceeds the rated voltage.

The valve member can be mounted for movement with the armature. The valve housing can define a flow path from a valve housing inlet to a valve housing outlet. The flow path can pass through the valve seat. With the valve member and armature in the first position, the valve member can seal against the valve seat and prevent flow through the flow path. With the valve member and armature in the second position, the valve member is spaced from the valve seat to allow flow through the flow path. A filter material can be seated within the flow path in the valve housing downstream of the valve seat and configured to prevent particles from flowing out of the valve housing with the armature and valve member in the second position. configured.

The air delivery device can include a pressure source. A pneumatic line can connect the pressure source to a connector configured to connect the insufflator to a trocar tube set for insufflating the patient's surgical cavity. The inlet of the valve housing can be connected to a separate branch from the pneumatic line to selectively allow or block pressure relief flow from the pneumatic line.

These and other features of the disclosed systems and methods will become more readily apparent to those skilled in the art from the following detailed description, taken in conjunction with the drawings.

To ensure that those skilled in the art to which this disclosure pertains will readily understand how to make and use the devices and methods of this disclosure without undue experimentation, preferred embodiments thereof are illustrated with reference to the specific drawings. This is described in detail below.

FIG. 1 is a schematic perspective view of an embodiment of a system constructed in accordance with the present disclosure showing an insufflation device providing insufflation to a patient. FIG. 2 is a schematic diagram of the system of FIG. 1 showing solenoids and valves connected to branches in the gas line extending between the pressure source and the trocar. FIG. 3 is a cross-sectional side view of the solenoid and valve of FIG. 2 showing the valve in a closed or flow-free position. 4 is a cross-sectional side view of the solenoid and valve of FIG. 3 showing the valve in an open position allowing flow therethrough; FIG. FIG. 5 is a cross-sectional plan view of the solenoid of FIG. 3 showing the permanent magnets. FIG. 6 is a functional block diagram for the system of FIG. 2. FIG. 7 is a voltage and state effect diagram for the system of FIG. FIG. 8 is a graph of voltage versus time illustrating an example of non-periodic valve cycling for the system of FIG.

Like reference numbers herein refer to the drawings where like structural features or aspects of the disclosure are identified. For purposes of explanation and illustration, a partial view of an exemplary embodiment of a solenoid valve system according to the present disclosure is shown in FIG. 2 and generally designated by the reference numeral 100, but is not limited thereto. Other embodiments of systems according to the present disclosure, or aspects thereof, are provided in FIGS. 1 and 3-8 as described. The systems and methods described herein can be used to operate valves, such as those in air delivery devices, and each solenoid has improved size, weight, and weight over more conventional solenoid valves. , and has efficiency.

Referring now to FIG. 1, an air delivery device or system 10 is illustrated. Insufflation device 10 includes an inlet channel 22 leading to first trocar 18 in communication with surgical cavity 16 of a patient, through which a flow of insufflation gas is delivered to surgical cavity 16 . Insufflation device 10 optionally includes an outlet flow path 24 leading from a second trocar 26 in communication with surgical cavity 16, through which, for example, a continuous flow of soot gases can be removed from surgical cavity 16. I can do it. Although shown and described herein in the exemplary context of a mechanically sealed trocar, those skilled in the art will appreciate that the systems and methods disclosed herein depart from the scope of this disclosure. It will be readily appreciated that it can be used with pneumatically sealed trocars and/or mechanically sealed trocars without the need for trocars.

Referring now to FIG. 2, the insufflation device 10 may include an external pressurized gas supply 40 connected to the insufflation device 10, and/or, for example, when the pressure of the external gas supply 40 is adjusted for insufflation. A pressure source 30 is included, which can include a pump 50 that can maintain the insufflation pressure if it is inadequate on its own. A pneumatic line or inlet channel 22 is configured to connect the insufflator 10 to the trocar tube set 20 for insufflating a pressure source 30 into the patient's surgical cavity 16 as shown in FIG. Connect to the connector 60 that has been installed. Valve 70 is in fluid communication with branch 72 of inlet flow path 22 to provide pressure relief to inlet flow path 22 . Solenoid 80 is operably connected to actuate valve 70 and controller 90 is connected to control solenoid 80 in turn for controlled actuation of valve 70.

Referring now to FIG. 3, a solenoid valve system 100 is described. System 100 generally includes a solenoid 80 and valve 70 shown in FIG. Solenoid 80 includes a coil 102 seated within a housing 104 and wound about longitudinal axis A. An armature or plunger 106 extends longitudinally, ie, along axis A, through the coil 102 and out of the first end 108 of the housing 104. Armature 106 includes a material responsive to an external magnetic field and is mounted within a bobbin 110 of housing 104 for longitudinal movement relative to coil 102 and housing 104 in response to the magnetic field of coil 102. Coil 102 is wound around the outwardly facing surface of bobbin 110 of housing 104, and the inwardly facing surface of bobbin 110 engages armature 106 as a sliding bearing surface.

With continued reference to FIG. 3, a latch member 112 is mounted to a second end 114 of the housing 104 opposite the first end 108. Latch member 112 includes a latching surface 116 configured to contact armature 106 with armature 106 in a retracted position, as shown in FIG. The latch member 112 is attached to the housing 104 using a screw 118 to adjust the axial position (relative to axis A) of the latch surface 116 within the housing 104 by rotating the latch member 112 relative to the housing 104. engaged with.

A plurality of permanent magnets 120 are distributed circumferentially around armature 106 at first end 108 of housing 104 to shape the magnetic field of coil 102. As shown in the cross section of FIG. 5, there are four permanent magnets 120 distributed circumferentially around the armature 106 in a symmetrical pattern to avoid imposing lateral forces on the plunger. . The polarity of each permanent magnet 120 is oriented radially relative to the longitudinal direction shown in FIG. As shown in FIG. 5, for each of the permanent magnets 120, the radially inner pole is magnetic south (denoted as S in FIG. 5) and the radially outer pole is magnetic north (denoted as N in FIG. 5). ).

Referring again to FIGS. 3-4, the valve member 122 or plunger is mounted for movement with the armature 106. Valve housing 124 defines a flow path from an inlet 128 of valve housing 124 to an outlet 126 of valve housing 128 . The flow path passes through the valve seat 130 of the valve housing 124 and is indicated in FIG. 4 by the thick flow arrows. Valve housing 124 includes a bearing member 132 whose inner surface acts as a sliding bearing surface for linear movement of valve member 122. Valve seat 130 is positioned between bearing member 132 and manifold portion 134 of valve housing 124 . The flow paths shown in FIG. 4 include passages 136, such as radial passages or the like, through each of the manifold portion 134, the valve seat 130, and the bearing member 132.

With valve member 122 and armature 106 in the first or closed position shown in FIG. 3, valve member 122 seals against valve seat 130 and prevents flow through the flow path. With the valve member and armature in the second or open position shown in FIG. 4, the valve member 122 is spaced from the valve seat 130 and is able to flow through the flow path. A filter media 138 is seated within the flow path within the outlet 126 of the valve housing 124 downstream of the valve seat 130. Filter media 138 may be pumped out of valve housing 124 by armature 106 and valve member 122 in the second or open position shown in FIG. 4, for example, during pressure relief from gas in surgical cavity 16 in FIG. The device 10 is configured to prevent particle flow, such as condensation, from exiting into the housing of the gas device 10. An inlet 128 of the valve housing 124 is connected to a branch 72 off the pneumatic line 22 (labeled in FIGS. 1 and 2) to selectively allow or block pressure relief flow from the pneumatic line 22. When valve 70 is open, compressed flow is diverted from the gas jet through filter media 138. The flow direction would be reversed in more traditional systems to allow the higher pressure to blow open the valve 70 by overcoming the net force of the spring 140 and the solenoid valve 80 below the holding opening voltage V _low do.

With continued reference to FIGS. 3-4, spring 140 is seated between the seat of bearing member 132 and valve member 122. As shown in FIGS. Spring 140 biases valve member 122 and armature 106 toward the open position shown in FIG. Therefore, if there is insufficient power to coil 102, the magnetic force acting on armature 106 is less than the bias of spring 140, causing valve member 122 to move to the open position shown in FIG. With sufficient power to coil 102, the magnetic force acting on armature 106 can overcome the bias of spring 140 and move valve member 122 to the open position shown in FIG. As discussed above, adjusting the position of the latching surface 116 of the latch member 112 within the housing 104 can be used to prevent over-compression of the sealing element 142 of the valve member 122 in the closed position shown in FIG.

3 and 8, solenoid valve system 100 includes a controller 90 (labeled in FIG. 2) that is operable to control coil 102 of solenoid valve 80. Connected. controller 90 causes controller 90 to apply actuation voltage V _high to coil 102 for a first time period t1 to actuate solenoid valve 80 (and valve 70) against the bias of spring 140; A lower voltage of a holding voltage V _low that is lower than the actuation voltage V _high is then applied to the coil 102 of the solenoid 80 to cause not only the armature 106 of the solenoid 80 but also the valve member 122 to operate during a second period t2. , including machine-readable instructions configured to maintain the open position shown in FIG. 4 against biasing. FIG. 8 shows a graph with three examples of the above-mentioned cycles of voltage over time. For example, the actuation voltage V _high may be 48 volts and the holding voltage V _low may be 5 volts. For example, applying the actuation voltage V _high may include applying 20 watts to the solenoid, and holding the solenoid against energization for a second period of time may include applying the holding voltage V _low , which involves applying 1 watt to the solenoid.

The coil 102 of FIGS. 3-4 is rated for continuous operation at rated voltage. The operating voltage V _high is above the rated voltage. This may be because the holding voltage V _low is below the rated voltage and because the first period t1 is relatively short. The controller 90 (of FIG. 2) causes the spring bias to relax and the voltage applied to the solenoid to drop below the holding voltage V _low during the period in which the coil 102 is cooled to the first temperature. After that, an actuation voltage is applied to the solenoid 80. Coil 102 is brought to a second temperature during a second period t2, eg, an operating temperature during the maintenance of solenoid valve system 100 in the closed position shown in FIG. The first period t1 at the operating voltage V _high is short enough that during the first period the coil 102 does not exceed the second temperature, i.e. the coil 102 heats up to the safe operating temperature of the coil. It only exceeds its rated voltage long enough to Although the operating voltage V _high is higher than the rated voltage, the first period t1 is short enough to apply the first voltage V _high without causing a failure mode to the coil 102 . Coil failure modes can include any of the following: dielectric breakdown, housing or bobbin melting or distortion, or armature seizure. At least one of the operating voltage V _high and the holding voltage V _low can be applied as a pulse width modulated (PWM) waveform, or an alternating current waveform, which it produces, and the average is the respective operating voltage and/or holding voltage V low. It is. Any suitable waveform can be used, such as alternating current waveforms produced by analog methods that take common forms including, but not limited to, square, triangular, sine, sawtooth, and half-sine. The waveform can also vary irregularly or dynamically, for example by digital signal generation, as long as the average effect results in a voltage. Continuous direct current can also be used.

When valve 70 is in the closed position shown in FIG. 3 and controller 90 detects excess pressure in air line 22 (labeled in FIG. 2), controller 90 reduces the voltage on coil 102 The holding voltage V _low can be lowered below thereby opening valve 80 under spring bias to the open position shown in FIG. 4 to relieve excess pressure in air line 22 . Similarly, if there is a power loss event that reduces the voltage to coil 102 to zero, valve 70 opens under spring bias to the open position shown in FIG. 4 and labeled in FIGS. 2-4. The pressure in the surgical cavity 16 (labeled in FIG. 1) is relieved in the patient through the insufflation line 22 and its branches 72.

The present disclosure describes solenoids and solenoid controllers that employ control with at least two voltage states, at least two of which are non-zero and applied to the solenoid coil. The first state is selected to be at a higher voltage than the second state and to have sufficient retraction force to actuate the valve. The first voltage is temporarily held until the solenoid plunger is displaced far enough for the second state voltage to hold the plunger in the retracted state. The second voltage is selected to maintain the retracted condition against a return force including a return spring or gas pressure. Additionally, the second state voltage is selected to reduce the required coil size and heat loss.

Finally, the third voltage state, which may be zero, reduces the holding force to a value less than the sum of the return springs and the pressure force acting on the poppet, returning the poppet to its pre-retraction position. .

In one embodiment, the first voltage is 24 volts and is applied for a duration of 1 second. The second voltage state that serves the hold function is 10 volts, and the third voltage state that serves the release function is zero. In all embodiments, the second voltage can be between 10% and 90% of the first voltage.

The individual voltages may be continuous direct current, or in other embodiments may be pulse width modulated with periodic average breakdown voltage steps. In yet other embodiments, the voltage steps may not be unique, but may be continuously decreasing voltages.

FIG. 6 shows a functional block diagram in which a solenoid controller provides the multi-step control voltages described above to a solenoid valve, which has the physical effect of permitting or disallowing gas flow to and from the valve. has. FIG. 7 illustrates the voltage conditions and effects described above.

The steady state current limit can be exceeded for short periods of time, and similarly, a duty cycle of less than 100% allows the steady state current limit to be exceeded. This is acceptable due to the time required for resistive heating to exceed the heat capacity of the coil material and raise the coil temperature to damaging levels.

The present disclosure allows an undersized coil, ie, a coil with a continuous rating of 10 volts, to be overdriven and exceed the continuous rating for a short time by applying, for example, 24 volts. The effect of overdriving the coil is a greater 24 volt force, which the continuous coil generates for a short time during the retraction phase, during which time the required force of the solenoid valve is highest. During a 1 second retraction, for example, the generated thermal power may be 240% of the allowed continuous power. This excess power is absorbed and accommodated by the deliberate design of the coil's thermal mass, implementing a lower power third voltage state during which coil cooling occurs.

Stated more simply, the systems and methods herein may employ solenoid coils that have an undersized power rating at the nominal system voltage, ie, an 11 watt rating in a 24 volt system. When driven at a full system voltage of 24 volts, the coil is briefly overdriven at 63 watts, producing substantially more power. Those skilled in the art will appreciate that the periods, wattages, and voltages provided herein as examples may instead be any suitable periods, wattages, or voltages for the given application. You will easily understand what you can do.

As described above and shown in the figures, the methods and systems of the present disclosure provide for actuation of valves, etc. in air delivery devices, and the solenoids that actuate the valves have improved size and weight over more traditional solenoid valves. , and has efficiency. Although the devices and methods of the present disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will appreciate that changes and/or modifications may be made without departing from the scope of the disclosure. It will be easy to understand.

Claims (22)

applying an actuation voltage to a solenoid valve for a first period of time to cause the solenoid valve to actuate against energization;
reducing a voltage applied to the solenoid to a holding voltage lower than the actuation voltage to hold the solenoid against the energization for a second period of time;
including;
The method wherein the solenoid has a coil to which the actuation voltage and holding voltage are applied, the coil is rated for continuous operation at a rated voltage, and the actuation voltage is greater than the rated voltage. 2. The method of claim 1, wherein the holding voltage is below the rated voltage. Applying the actuation voltage to the solenoid maintains the holding voltage during a period when the energization is relaxed and the voltage applied to the solenoid cools the coil to a first temperature. 2. The method of claim 1, wherein the coil is ramped to a second temperature during the second period of time. 4. The method of claim 3, wherein the first period is short enough such that the coil does not exceed the second temperature during the first period. the solenoid is operably connected to a valve having an open position for allowing flow through the valve and a closed position for preventing flow through the valve, the biasing causing the valve to energizing the valve to an open position and actuating the solenoid against the bias actuating the valve to the closed position and retaining the solenoid against the bias. 2. The method of claim 1, wherein the method comprises: maintaining the closed position in the closed position. further comprising reducing a voltage below the holding voltage in response to excess pressure in the air line, thereby opening the valve to the open position under the bias to open the valve in the air line. 6. The method of claim 5, wherein the excess pressure of the air is released. 6. The method of claim 5, further comprising reducing the voltage to zero in a power loss event, thereby opening the valve under the bias to the open position to relieve pressure within the surgical cavity of the patient. Method described. 6. The method of claim 5, further comprising filtering flow through the valve in the open position to reduce or prevent particles from passing through the valve. 2. The method of claim 1, wherein at least one of the actuation voltage and the holding voltage is applied as an alternating current waveform averaged over the respective actuation voltage and/or holding voltage. The operating voltage is higher than the rated voltage, but the first period is short enough to apply the first voltage without causing a failure mode to the coil, and the failure mode is a dielectric breakdown, housing or bobbin failure mode. 2. The method of claim 1, comprising at least one of melting or distorting the armature, or seizing the armature. 2. The method of claim 1, wherein the actuation voltage is 48 volts and the holding voltage is 5 volts. Applying the actuation voltage includes applying 20 watts to the solenoid, and holding the solenoid against the energization for a second period includes applying 1 watt at the holding voltage. 2. The method of claim 1, comprising applying a voltage to the solenoid. a coil seated within the housing;
an armature extending longitudinally through the coil and exiting the first end of the housing, the armature including a material responsive to an external magnetic field; an armature mounted within the housing for movement relative to the housing in response to a magnetic field;
a latch member mounted on a second end of the housing and configured to contact the armature with the armature in a retracted position;
a plurality of permanent magnets distributed circumferentially around the armature at a first end of the housing;
Equipped with a solenoid. 5. The latch member is threadably engaged with the housing to adjust the axial position of the latch surface within the housing by rotating the latch member relative to the housing. The solenoid according to item 13. 14. The solenoid of claim 13, wherein there are four permanent magnets distributed circumferentially about the armature. 16. The solenoid of claim 15, wherein the polarity of each of the permanent magnets is oriented radially with respect to the longitudinal direction. 17. The solenoid of claim 16, wherein for each of the permanent magnets, the radially inner pole is magnetic south and the radially outer pole is magnetic north. 14. The solenoid of claim 13, wherein the coil is wound around an outwardly facing surface of a bobbin of the housing, and an inwardly facing surface of the bobbin engages the armature as a sliding bearing surface. a coil seated within the housing;
an armature extending longitudinally through the coil and exiting the first end of the housing, the armature including a material responsive to an external magnetic field and responsive to the coil and the magnetic field of the coil; an armature mounted within the housing for movement relative to the housing;
a solenoid comprising; and
a controller operably connected to control the coil, the controller including machine readable instructions;
Equipped with
The machine readable instructions cause the controller to:
applying an actuation voltage to the coil to actuate the solenoid against energization during a first time period, and reducing the voltage applied to the solenoid to a holding voltage below the actuation voltage; , configured to hold the solenoid against the biasing for a second period of time;
A system in which the coil is rated for continuous operation at a rated voltage, and the operating voltage is greater than the rated voltage. a valve member mounted to move with the armature;
a valve housing defining a flow path from an inlet of the valve housing to an outlet of the valve housing, the flow path passing through a valve seat, the valve member in a first position; The armature seals the valve member against the valve seat to prevent flow through the flow path, and the valve member and armature in a second position seals the valve member against the valve seat. a valve housing spaced from and allowing flow through the flow path;
20. The system of claim 19, further comprising: seated within the flow path in the valve housing downstream of the valve seat and configured to prevent the flow of particles out of the valve housing with the armature and valve member in the second position; 21. The system of claim 20, further comprising a filtration material. Further comprising an air supply device, the air supply device comprising:
a pressure source;
a pneumatic line connecting the pressure source to a connector configured to connect the insufflation device to a trocar tube set for insufflating a surgical cavity of a patient, the inlet of the valve housing being , an air line connected to a branch from the pneumatic line for selectively allowing or blocking pressure relief flow from the air line;
21. The system of claim 20, comprising:

Images